1. Field of the Invention
The present invention relates to a reproducing method, a reproducing apparatus, a recording and reproducing apparatus, and a magnetic recording medium that are all adapted to a high density recording.
2. Description of the Related Art
In recent years, the recording density of magnetic recording media, such as magnetic recording tapes or magnetic disks, has been remarkably increased. Due to such high recording density, various technologies regarding recording and reproducing apparatuses have been conceived, and been in practical use. For example, MR (Magneto Resistive) heads are used as reproducing heads, and a technology for improving the interface between a recording medium and heads is proposed. Furthermore, in a signal processing technology, a PRML system, which combines PR (partial response) system and an ML (Maximum Likelihood) system, is applied to recording and reproducing apparatuses for processing recording media such as magnetic disks, digital video tapes, magnetic tapes for computer backup and optical disks. This PRML system makes it possible to compensate the deterioration in the S/N ratio of recording media because of the high recording density (see U.S. Pat. No. 6,337,889).
Note that U.S. Pat. No. 6,337,889, which is incorporated herein by reference, also discloses the above technology, wherein U.S. Pat. No. 6,337,889 corresponds to Japanese Unexamined Patent Application Publication No. 2002-157827.
Conventionally, in a typical type of magnetic recording media, ones having a magnetic layer containing hexagonal ferrite are used. These media exhibit excellent reproducing output and low noise characteristics in high density recording. However, hexagonal ferrite has a magnetization component of a vertical direction in an in-plane orientation or a random orientation, derived from a crystal structure thereof. Therefore, their isolated inversion reproducing wave has a unique waveform where respective isolated inversion reproducing waveforms in the in-plane orientation and in the vertical direction are added. Consequently, the PRML signal processing system (herein, EEPR4ML: PR(1, 2, 0, −2, −1)) cannot be applied to the above magnetic recording media. This is because the PRML signal processing system is optimized for magnetic recording media in which data is recorded by means of the magnetization in the in-plane orientation. This can be a disadvantage.
Taking this disadvantage into account, the present invention has been conceived. An object of the present invention is to provide a reproducing method and a reproducing apparatus which both allow the PRML signal processing system to be applied suitably to magnetic recording media in which a magnetic layer containing hexagonal ferrite is formed. An additional object of the present invention is to provide a magnetic recording medium that undergoes the PRML signal processing system appropriately with the above method and/or the above apparatus.